Switching type chargers are widely used in smart phones and tablet computers due to their relatively small size, high efficiency, and fast charging speeds for charging a battery. An external input power supply (e.g., an adapter, USB interface, etc.) for the charger usually has limitations on its output power and output current. When the charging current of a charger is too high, the input power supply may enter a current-limiting state, which can possibly result in abnormal charger operation.